Field of the Invention
The present invention relates to a technique of improving a fuel supply apparatus for a general purpose engine.
Description of the Related Art
For example, Japanese Laid-Open Patent Publication No. 60-249655 discloses a typical fuel supply apparatus for an engine. The fuel supply apparatus for the engine includes a negative pressure pipe extending from a carburetor to a combustion chamber of the engine, a connection pipe connecting the negative pressure pipe and a float chamber of the carburetor, a control valve such as a solenoid valve provided in this connection pipe, an air fuel ratio sensor for detecting the air fuel ratio of an exhaust gas discharged from a combustion chamber of the engine, and a control unit for controlling the control valve based on a detection signal of the air fuel ratio sensor.
When the control valve is closed, the float chamber is placed in a basic state (non-depressurized state) where the pressure in the float chamber is not reduced. When the control valve is opened, the pressure difference between the negative pressure pipe extending from the carburetor to the combustion chamber and the float chamber of the carburetor becomes small. As a result, it is possible to control the air fuel ratio in the lean direction, from the air fuel ratio in the basic state where the float chamber is not depressurized.
However, the pressure reduction level in the float chamber is affected by the negative pressure of the negative pressure pipe extending from the carburetor to the combustion chamber. That is, the pressure in the float chamber is simply decreased to the level of the negative pressure of the negative pressure pipe. There is a room of improvement in controlling the air fuel ratio of the exhaust gas from the engine much more accurately and much more finely.